Island



UNITED STATES PATENT OFFICE.

EDIVIN M. CARHART, OF PROVIDENCE, RHODE ISLAND.

B U RG LAR-ALARM SPECIFICATION forming part of Letters Patent No. 410,683, dated September 10, 1889. Application filed December 26, 1888. Serial No. 294,678. (No model.)

To all whom it may concern:

Be it known that I, EDWIN M. CARHART, a citizen of the United States, residing at Providence, in the county of Providence and State of Rhode Island, have invented certain new and useful Improvements in Short-Circuit Springs for Electrical Alarms; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

My invention relates more particularly to short-circuit springs for electrical alarms;- and it consists, essentially of an electrically-connected shell or casing having aspring-actuated contact-pin mounted therein, combined with an electrically-001mected metallic plate insulated from the shell and having an enlarged opening, through which an end of the pin extends, the whole when mounted being so arranged that the pin and contact-plate are insulated from each other when in the normal position. A place well adapted for the use of my improvement is, say, a door leading to a room or vault in which valuables are kept, in which case the electrically-connected shell and plate are mount-ed in the door-frame, an end of the pin extending through (but not touching) the plate and bearing against an edge of the closed door. Now, in the event of the door being opened the pin is instantly forced into engagement with the contact-plate through the medium of the spring, thereby closing the electric circuit and automatically turning in an alarm at the station or headquarters.

In the accompanying sheet of drawings, Figure 1 represents in reduced scale a complete circuit, in which two doors are electrically connected. It also indicates an office or headquarters-station, in which a galvanometer is mounted. Fig. 2 is a sectional view taken through the center of my improved short-circuit spring connection, the several parts being in the normal position. Fig. 8 is a similar view of the parts, the door being open and the center contact pin or spindle being in enthe contact-plate about to be described.

gagement with the electrically connected plate, thereby closing the circuit and by means of suitable connections located in the main circuit sounding an alarm or otherwise indicating that the continuity of the circuitis interrupted; and Fig. 4 is a front View of the contact-plate.

Referring again to the drawings, A designates my present improvement as a whole.

a indicates the metallic tubular shell, of brass or other suitable metal, open at the front end and closed at the other. A pin 0 is mounted within the shell a, the same extending through the rear end of said shell, and is provided with a stop 0 Intermediate of the ends of the pin 0 is formed an enlargement or metallic piston c, which fits the bore of the tube. The front portion of the piston is substantially cone-shaped, and terminates in the plain portion of the pin which extends through I1 inclosed spiral spring e, engaging the rear end of the shell and at the same time bearing against the under side of the piston, acts to force the pin forward to engage the contactplate, thereby automatically closing the electric circuit; A stop 0 serves to limit the forward movement of the pin. In the construction of the shell a, I preferably enlarge the front end thereof, so as to form a circular flange 7L, thereby readily adapting it to be electrically connected with one of the conducting-wires w; or the wire may be soldered to the shell.

7) indicates the contact-plate, made of suitable conducting material, as brass, 850., the same having an enlarged central hole I) therein, through which the reduced front portion of the pin 0 freely passes, (see Fig. 2,) although permitting the cone-shaped portion 0' to engage the plate, as shown in Fig. 3, whenever the door or restraining element is removed. Screws passing through holes formed in the extremities of the plate I) afford means for attaching it to a door-frame, &c., as (1 By referring to Figs. 3 and 4 it will be seen that the said plate is so formed that it may be readily let into a door-frame, &c., by simply boring shallow holes therein with bits having a corresponding size; or the plate may be circular, as indicated by the broken line b (See Fig. 4.) The casing itself maybe also as readily attached to the door-frame by'boring a hole m therein, the same being enlarged or counterbored at its outer end or face, as 'm', to form a seat for the flange h of the shell, as clearly shown. The counterbored portion m of the hole also forms a non-conducting.

space or chamber intervening between said shell and. the plate, thereby insulating the parts from each other.

Themanner of operation is substantially as follows, assuming the shell and plate to be mounted in a door-frame, as diand connected each with a conducting-wire w, and havingv the outer end of the pin or piston-rod 0 passing loosely through the plate b, and being in engagement with and pressing against the door d, as shown in Fig. 2, the electric circuit ythus being open: Now, upon opening the door or otherwise removing the pressure from the end of the pin, the spring 6 instantly acts to force the piston and pin endwiseuntil the enlarged portion of the latter, engages andis arrestedby the contact-plate b, as shown in At the instant of the engagement of Fig. 3. the parts a and b the continuity of. the electric circuit is affected, thereby causing an alarm to be sounded; or the result may be indicated by a corresponding movement ofthe pointer of a suitably-mounted galvanometer g, located in the circuit.

I. would state that the two poles or conducting-wires u; may be connected. with and form a part of a burglar-alarm systemhaving.

a headquarters or station communicating with a series of buildingsor rooms, in which the several doors and Windows thereof are provided with my improvement.

It is obvious that the arrangement of the conducting-wires, battery, &c., may be such that my improved short-circuit spring can be efficiently used either for an openforv closed circuit. P

I claim as my invention-- 1. A short-circuit spring for bu rglar-alarlns, consisting of an electrically-connected shell or casing, a spring-actuated contact-pin provided with a cone-shapedhead mounted within the shell, and an electrically-connected plate provided with an enlarged. central opening through which the outer end of said pin slightly extends, thereby, when in its normal position, forming an annular space around the 3. The combinatiomwith the electrically-- connected shell a and'apertured plate 12, constructed and arranged substantially as shown and described, of the spring-actuated contact-pin c, ha ving a cone-shaped head portion extending slightly through said. plate, and forming, when. thus in its normal open-circuit position, an annular space around the pin, but when the pressure upon the pin is removed the spring forces the head of thepin into engagement with. the plate, thereby closing the circuit, substantially as hereinbefore set forth.

In testimony whereof I-have affixed my signature in presence of two witnesses.

EDWIN M. OARHART.

Witnesses! CHARLES HANNIGAN, Gno; H. Rnn ne'ron. 

